Motor hand area

The lateral, convex side of the primary motor cortex is arranged from top to bottom in areas that correspond to the buttocks, torso, shoulder, elbow, wrist, fingers, thumb, eyelids, lips, and jaw.

The arm and hand motor area is the largest, and occupies the part of precentral gyrus between the leg and face area.

These areas are not proportional to their size in the body with the lips, face parts, and hands represented by particularly large areas. Following amputation or paralysis, motor areas can shift to adopt new parts of the body.

Using functional magnetic resonance imaging (fMRI) Yousry et al. evaluated the anatomical location of the motor hand area. The segment of the precentral gyrus that most often contained motor hand function was a knob-like structure, that is shaped like an omega or epsilon in the axial plane and like a hook in the sagittal plane. On the cortical surface of cadaver specimens this precentral knob corresponded precisely to the characteristic 'middle knee' of the central sulcus that has been described by various anatomists in the last century.

They were then able to show that this knob is a reliable landmark for identifying the precentral gyrus directly. They, therefore, conclude that neural elements involved in motor hand function are located in a characteristic 'precentral knob' which is a reliable landmark for identifying the precentral gyrus under normal and pathological conditions. It faces and forms the 'middle knee' of the central sulcus, is located just at the cross point between the precentral sulcus and the central sulcus, and is therefore also visible on the cortical surface ¹⁾.